The invention relates to a casting device and to a method of venting casting devices.
In both die casting and injection molding air voids must be avoided in the finished part to ensure high quality thereof. Achieving this necessitates reliable venting of not only any air from the die cavities but also any gas escaping from the molten casting mass.
For venting gases entrapped in the die cavity, venting means for casting devices are known from prior art featuring so-called cooling blocks. In this arrangement each cooling block arranged at the end of a vent passage connecting the die cavity has the task of venting the gases whereby the molten casting material is cooled and solidified on having entered the cooling block. Another venting system features valve devices in the vent passage, two basic types of which are known, each comprising a vent valve with a reciprocating closure member for closing off the vent passage. Whilst in the first type the closure member is activated remotely, in the second type it cooperates with a force transducer directly actuated by the casting material urged from the cavity into the vent passage in exploiting its kinetic energy.
Known from EP 0 612 573 is valve means for venting casting dies provided with a vent passage, a vent valve in the latter and an actuator for closing the vent valves. The actuator comprises a force transducer responding to the casting material entering the the vent passage from the cavity, it mechanically communicating with the movable closure member of the vent valve. In this arrangement the force transducer is configured as a pusher the working stroke of which is limited to a fraction of the travel of the movable closure member in closing off the vent valve. In addition, the closure member of the vent valve has idle movement exceeding the working stroke of the force transducer and the actuator comprises a force transmitter for communicating the activating pulse from the force transducer to the movable closure member of the vent valve.
To boost productivity casting devices have been developed which feature a casting chamber, the outlet of which can be closed off at least partially by a closure member with the advantage of shortening the cycling time since the casting chamber is shot either before or when the die is closed. The drawback with shortening the cycling time is, however, the added risk of air voids.
Known from DE 199 14 830 A1 is a casting device provided with a closure member. This casting device comprises a fixed first die half and a movable second die half, both of which define between them the die cavity to be shot with the molten metal. The first die half is provided with a casting chamber housing a casting plunger guided therein. The inlet end of the casting chamber features a metering orifice whilst the outlet of the casting chamber is connected to the die cavity by a runner. Arranged in the region of the casting chamber and connected to a hydraulic system by a piston rod is a bevelled valve for closing off the outlet of the casting chamber. A vent passage leads out of the cavity of the die communicating with a means for developing a vacuum and with a vacuum shutoff valve. Casting firstly requires the die cavity and the runner to be evacuated via the shutoff valve, after which the molten metal is shot into the casting chamber. After metering of the casting material the casting plunger travels via the metering orifice into the casting chamber until the chamber is shot with the molten metal. It is not until the casting chamber is shot 100% with the molten metal that the valve is opened so that the molten metal can enter the die cavity via the runner.